Internal combustion engine exhaust system equipped with pollution reduction systems

ABSTRACT

Exhaust system for an internal combustion engine ( 1 ) of a motor vehicle which is equipped with a first oxidation catalytic converter or precatalytic converter ( 4 ) positioned near the outlet of gas from the engine, and with a particulate filter ( 9 ) associated with a second oxidation catalytic converter ( 8 ) these being positioned downstream of the precatalytic converter. It comprises first means for generating an increase in the temperature of the gases leaving the engine ( 1 ), second means for generating an exothermal reaction in the precatalytic converter ( 4 ) and third means ( 5 ) for generating an exothermal reaction in the catalytic converter ( 8 ) so as to split the burden of generating the increase in exhaust gas temperature required for regenerating the particulate filter ( 9 ) between the engine, the precatalytic converter and the catalytic converter.

The invention relates to a motor vehicle engine gas exhaust line equipped with pollution control systems.

The majority of pollutants produced by combustion in a motor vehicle engine—diesel or gasoline—are unburned hydrocarbons, nitrogen oxides (nitrogen monoxide NO and nitrogen dioxide NO₂), carbon oxides (carbon monoxide CO), and, in diesel engines and direct injection gasoline engines, solid carbon particles.

In order to comply with international environmental standards, it is imperative to control HC, CO, NOx, and particulate emissions, and exhaust after-treatment technologies are indispensable.

Motor vehicle pollution control makes use of various after-treatment systems to remove the pollutants produced by the engine: catalysts, and the particulate filter for diesel engines.

The particulate filter removes solid particles present in the exhaust gas of diesel engines by filtration. Once trapped inside the filter, the particles must be removed periodically by raising the temperature to 450 to 700° C. inside the filter, resulting in their combustion. This operation is commonly called “regeneration” of the particulate filter. Traditionally, the energy needed for regeneration is supplied by raising the temperature of the exhaust gas. However, expecting the engine to provide such a temperature poses problems, in particular for the highest temperatures, between 550 and 700° C.

Traditionally, the extra exhaust energy relative to normal engine operation is provided by using post-injections, i.e., late fuel injections made after top dead center in the cycle, or by degradation of the combustion output.

When using a post-injection, the latter can burn completely or partially in the engine, generating an increase in exhaust gas temperature, or, if it is done late enough it can produce increased quantities of exhaust CO and HC that oxidize upon reaching the oxidation catalyst in order to generate heat.

This method produces severe thermal stress on the catalyst closest to the engine, which undergoes a sharp increase in temperature with each regeneration. In addition, the turbocompressor and the exhaust manifold are also subjected to high temperatures. Finally, methods using heat from the engine result in diesel fuel dilution of engine lubrication oil, which reduces engine life expectancy.

Using diesel fuel injection into the exhaust can solve most of these problems. In this case, the heat from the engine is greatly reduced, and heat is generated by burning the diesel fuel introduced into the exhaust on the catalyst upstream of the particulate filter. Oil dilution is then greatly reduced, along with the thermal stresses on the exhaust manifold and the turbocompressor.

This technology offers a specific advantage when the oxidation catalyst is split into one part near the engine exit (known as a “pre-catalyst”) and one part further removed from this exit, e.g., under the vehicle body (known as a “catalyst”). In this case, injecting diesel fuel between the two catalysts places the thermal demand only on the second catalyst during regeneration, with the pre-catalyst then being dedicated solely to oxidizing the HC and CO exiting the engine.

The major disadvantage of this technology is the very high thermal demand on the catalyst that generates the exotherm (up to 400 or 500° C. exothermic heat) and the need for a very high HC-treatment capacity for the latter so as to avoid fumes and odors in the exhaust.

The purpose of the invention is thus to propose a strategy, to be used in an exhaust line comprising a catalyst associated with a particulate filter, that aims to generate a high enough temperature upstream of the particulate filter to produce complete combustion of the particles without placing excessive demand on the engine or the catalyst.

To this end, an object of the present invention is a motor vehicle internal combustion engine gas exhaust line equipped with a first oxidation catalyst, or pre-catalyst, placed near the engine exhaust exit, and a particulate filter associated with a second oxidation catalyst placed downstream of the pre-catalyst. According to the invention, it comprises first means for raising the temperature of the gas exiting the engine, second means for generating an exothermic reaction in the pre-catalyst, and third means for generating an exothermic reaction in the second catalyst, so as to distribute the task of raising the exhaust gas temperature, required for regenerating the particulate filter, between the engine, the pre-catalyst and the second catalyst.

According to other advantageous characteristics of the invention:

The means for raising the temperature of the gas exiting the engine are capable of producing a degradation in combustion efficiency.

The degradation in combustion efficiency is achieved by retarding the main fuel injection, i.e., with an injection that is later relative to the top dead center of the cycle.

The main injection is retarded by 2 to 20° crank angle relative to a normal injection.

The degradation in combustion efficiency is achieved by reducing the quantity of air taken into the engine.

The means for raising the temperature of the gas exiting the engine make it possible to obtain gas temperatures between 200 and 650° C. upstream of the pre-catalyst.

The means for generating an exothermic reaction in the pre-catalyst are capable of initiating a fuel post-injection phase in the engine.

The post-injection is late and is between 90 and 240° crank angle.

The temperature of the exothermic reaction in the pre-catalyst is between 20 and 200° C.

The means for generating an exothermic reaction in the catalyst is a fuel introduction device located between the pre-catalyst and the catalyst.

The temperature of the exothermic reaction in the catalyst is between 20 and 300° C.

The three means for heating the exhaust gas are activated successively according to the difference between the temperature of the gas at the engine exit and the temperature needed at the upstream end of the particulate filter in order to carry out the regeneration thereof

At least two of the means for heating the exhaust gas are activated simultaneously.

The two exothermic reactions are produced simultaneously and controlled so as to achieve the best compromise between HC treatment and fuel consumption.

At high engine speeds and medium and high loads, the means for raising the temperature of the gas exiting the engine are given precedence over the other two means for heating the gas.

Control of the heating means is preset by mapping.

Control of the heating means is by closed-loop regulation.

Regulation uses one or more temperatures detected by sensors at various points in the exhaust line.

Regulation of the means that generate the exothermic reactions takes the exhaust gas flow rate into account.

When the means for raising the temperature of the gas exiting the engine operate by retarding the main injection, regulation acts on the retard angle thereof, with respect to a 90° crank angle.

In order to regulate the exothermic reaction on the pre-catalyst, the quantity and timing of the post-injection are adjusted.

In order to regulate the exothermic reaction on the catalyst, the average flow rate of the fuel injected into the exhaust is controlled.

In order to control the strategy for raising the gas temperature, the preset mapped and closed-loop regulation control modes are combined. For example, mapped regulation of engine heating is coupled with regulation by sensor of the exothermic reactions in the pre-catalyst and catalyst.

During the regeneration phase, the means for heating the exhaust gas are used continuously, intermittently, or in continuously variable quantities.

The second catalyst is placed upstream of the particulate filter or integrated onto the same support.

The fuel has an additive to promote particulate filter regeneration.

Other characteristics and advantages of the invention will become clear in the following description, given as a guide, with reference to the attached drawings, in which:

FIG. 1 is a block diagram of an exhaust line according to the invention.

FIG. 2 is a graph of temperatures at different points in the exhaust line, as a function of engine speed.

FIG. 3 is a graph illustrating an example of a change in heating mode when there is a reduction in engine load.

FIGS. 4, 5 and 6 illustrate examples of heating mode distributions over the engine field.

FIGS. 7 and 8 are control examples for the various heating means, and

FIG. 9 shows examples of injection sequencing.

The block diagram in FIG. 1 illustrates an example of an exhaust line according to the invention.

As is known, this line comprises an engine 1, e.g., a four-cylinder diesel engine, with an exhaust gas manifold 2 and a turbocompressor 3 at its exit, leading into the exhaust line.

This exhaust line has a first catalyst, or pre-catalyst 4, placed near the engine exhaust exit that treats the HC and CO emissions from the engine.

At the pre-catalyst 4 output, a device 5 introduces fuel, e.g., diesel fuel, into the exhaust line.

This device comprises, for example, control means for injection 6 from a fuel tank 7 of the vehicle or from the fuel supply system of the vehicle.

The fuel introduction device 5 is located between the pre-catalyst 4 and a second catalyst 8 associated with a particulate filter 9.

The catalyst 8 and the particulate filter 9 are located far enough from the means 5 for introducing fuel into the exhaust line to allow for good homogenization of the exhaust/fuel mixture.

According to the invention, we aim to generate a high temperature, between 400 and 800° C. (preferably between 450 and 700° C.), upstream of the particulate filter without placing an excessive demand on the engine or the catalyst to achieve regeneration of said filter.

In order to do this, the strategy consists in distributing the task of raising the temperature between the engine, the pre-catalyst and catalyst.

For this purpose, we generate an increase in the temperature of the gas exiting the engine 1, and exothermic reactions in the pre-catalyst 4 and the catalyst 8.

The increase in the temperature of the gas exiting the engine 1 can be achieved by degrading combustion efficiency, e.g., by retarding the main injection, i.e., with a later injection relative to top dead center (TDC), by a post-injection that burns completely in the engine, by intake flow control, or any combination of these known means.

FIG. 9 b shows an injection sequence with the main injection retarded; it can be seen that, relative to a traditional injection like that shown in FIG. 9 a, the main injection is offset by 2 to 20° crank angle.

This is meant to produce an exhaust temperature between 200 and 650° C. upstream of the pre-catalyst 4. In the most common engine operating conditions, this temperature range will be between 250 and 400° C. This corresponds to a temperature increase of 50 to 350° C. over the non-regeneration operating mode.

The exothermic reaction on the pre-catalyst 4 will be produced by using a post-injection, preferably a late one, in order to reduce engine oil dilution. FIG. 9 b shows a post-injection of this kind, between 90 and 240° crank angle, whereas a traditional post-injection (FIG. 9 c) is between 20 and 90° crank angle. Preferably, this late post-injection will be between 120 and 180° crank angle.

The closer a post-injection is to the main injection, the more heat it generates coming out of the engine. Conversely, a later post injection generates CO emissions due to incomplete combustion, and hydrocarbons. The later the post-injection, the lower the quantity of heat produced and the more HC in the exhaust gas.

These CO and HC emissions are oxidized upon arriving on the pre-catalyst, and generate heat. In order to keep the latter from being subjected to temperatures that are too high, the temperature of the exothermic reaction thus produced will be between 20 and 200° C., in most cases between 50 and 150° C.

The exothermic reaction on the catalyst 8 is generated by the fuel introduction device 5, which sends hydrocarbons into the catalyst whose oxidation will cause significant heat to be released. A temperature between 20 and 300° C. is targeted for the exothermic reaction thus created, and in most cases it will be between 50 and 200° C.

The diagram in FIG. 2 shows the output temperatures for each of the elements that help to heat the exhaust line, as a function of engine speed: θ1 is the temperature at the turbocompressor 3 outlet during normal engine operation, i.e., excluding particulate filter regeneration phases; θ2 is the temperature at the turbocompressor outlet during a regeneration phase, θ3 is the temperature at the pre-catalyst 4 outlet, and θ4 is the temperature at the catalyst 8 outlet. Of course, θ2, θ3, θ4 are the temperatures reached according to the teaching of the present invention. Zone Z, shown in gray, is the temperature zone in which particulate filter regeneration can occur.

It can be seen that the amplitude of the curves varies according to the engine operating ranges. In the zones in which the engine is operating under a heavy load, e.g., the end of the cycle as illustrated in the figure, just one or two of the three means are adequate to produce the required temperature increase. Consequently, it is possible to control activation of the various heating means.

FIG. 3 illustrates the possible activation modes for these various means when the engine load decreases during particulate filter regeneration. When the load decreases, the temperature θ5 at the engine outlet also decreases.

In part (1) of the graph, this temperature is nevertheless high enough to ensure that the temperature θ7 upstream of the particulate filter can enable the regeneration thereof with no need for additional heating.

In part (2) of the graph, the engine output temperature becomes too low to ensure regeneration by itself. Fuel is then injected into the exhaust in order to start an exothermic reaction in the catalyst 8, and the temperature θ9 at the outlet thereof increases so that θ7 remains in the regeneration zone.

In part (3), after a new decrease in the engine output temperature θ5, we additionally start an exothermic reaction in the pre-catalyst 4 so as to increase the temperature θ8 at the outlet thereof.

Finally, if the engine temperature θ5 decreases again, as in part (4) of the graph, we additionally start the means provided for raising the engine temperature θ6.

By successively activating the various exhaust gas heating means, we observe that the temperature θ7 upstream of the particulate filter has remained substantially constant. Instead of successive activation, it may be adequate to provide for simultaneous activation of two or three heating means while modulating their effects. The exothermic reactions in the catalyst 8 and the pre-catalyst 4 can be activated simultaneously, but in variable proportions to reach the best compromise between HC emissions treatment, for which pre-catalyst heating is preferable while fuel consumption is penalized, which is less significant when heating the catalyst by injecting fuel into the exhaust.

FIGS. 4 to 6 show distributions of this kind over the engine field. In zone A of the graphs in FIGS. 4, 5 and 6, normal exhaust heating by the engine is adequate, and no additional strategy is employed.

In the strategy example shown in FIG. 4, we successively trigger exothermic reactions in the catalyst 8 (zone B) and the pre-catalyst 4 (zone C), whereas in the example shown in FIG. 5, the two exothermic reactions are produced simultaneously in both zones B and C and controlled so as to reach the best compromise between HC treatment and fuel consumption.

In zone D of the two graphs, engine heating is also activated.

In addition to these transitions, at high engine speeds and medium and high loads, the high exhaust gas flow rates make it more difficult to generate exothermic reactions without raising HC emissions too high; thus, engine heating is given priority over the other means (zone E in the graphs).

In the third strategy example shown in FIG. 6, exotherm generation is used only in the zones of the engine field in which engine heating is difficult and is a source of fuel dilution of engine oil (zone F). In the other zones (zone G), heat is generated solely by the engine.

Control of the heating means can be done in various ways.

For example, it can be preset, by mapping. One point in the engine speed/load curve always corresponds to the same value for each of the heating means. In this case, no specific sensor is needed.

Or it can be done by closed-loop regulation, based on one or more temperatures detected by sensor at various points in the exhaust line. The temperatures can be detected between the turbocompressor 3 exit and the pre-catalyst 4, between the pre-catalyst 4 and the catalyst 8, and downstream of the catalyst 8. Along with these, an additional point can be recorded downstream of the particulate filter 9.

In addition to temperature, the exhaust gas flow rate can be taken into account in regulating the means that generate the exothermic reactions. This flow rate can be measured or estimated.

As far as engine heating is concerned, if the latter is done by means of a post-injection, regulation will act on the quantity and timing thereof. If it is done by retarding the main injection, regulation will act on the retard angle and quantity thereof, with respect to a 90° crank angle.

Likewise, the quantity and timing of the post-injection can be adjusted to produce the exothermic reaction on the pre-catalyst.

Controlling the average flow rate of the fuel injected into the exhaust will also serve to modulate the exothermic reaction of the catalyst. This can be controlled based on the temperature upstream of the particulate filter.

Lastly, these control modes can also be combined.

For example, FIG. 7 shows a control mode in which mapped regulation of engine heating is coupled with sensor-regulated exothermic reactions: the temperature T1 upstream of the catalyst is measured and compared to the temperature T2 we want to obtain upstream of the particulate filter; the quantities of heat that must be created in the pre-catalyst (Q1) and the catalyst (Q2) are continuously adjusted in this way.

In FIG. 8, the temperature T3 upstream of the particulate filter is what is used for regulation, while the quantities of heat in the pre-catalyst (Q3) and the catalyst (Q4) have on/off control.

Of course, these examples are non-limiting, and other control modes for the heating means could be chosen without departing from the scope of the invention.

Likewise, the heating means can be used during the regeneration phase in the various applicable regulation modes continuously, intermittently, or in PID-type continuously variable quantities, using the formula:

Heat needed=Prepositioning [engine point]+K_(p)×(Ttarget-Tmeasured)+K_(i)×

∫(Ttarget−Tmeasured)+K_(d)×|Ttarget−Tmeasured|/(Ttarget−Tmeasured)×d(Ttarget−Tmeasured)/dt

The injected quantity is calculated thusly, by adding together: a quantity dependent on the engine point, a quantity proportional to the difference between the temperature reached and the target temperature, a quantity proportional to the derivative with respect to time of the difference between the temperature reached and the target temperature (which will be subtracted if the difference between the temperature reached and the target temperature is positive, or added if the difference is negative), and a quantity proportional to the integral of the difference over a time much greater than the temperature variation scale.

To further clarify, the various heating means can use the same type of regulation or different modes.

As is well known, the various injections used to produce the exothermic reactions can also be split into multiple injections.

From the above description it is clear that by distributing the task of raising the temperature in the exhaust line between three elements of this line, the invention makes it possible to minimize stresses on all the elements of this line.

Dilution of oil inside the engine and the temperature at the exit thereof will be reduced.

The pre-catalyst, which helps primarily with pollution control on a regulatory cycle, will not be subject to accelerated aging.

Since the exothermic reactions in the two catalysts are limited, their material needs no specific formulation relative to those currently in use.

The quantity of HC to be treated by the catalysts is low, particularly for the catalyst located upstream of the particulate filter, which receives the gas injected into the exhaust in good conditions (hot upstream gas). The risk of parasitic HC emissions (fumes, odors) is therefore lower.

This strategy also makes it possible to reduce thermal losses and thus improve fuel consumption during particulate filter regeneration phases. That is, the heat generated by exothermic reaction on the catalysts results in less thermal loss than that created in the engine.

Lastly, this strategy allows improved regeneration efficiency in all conditions, and particularly in low-load zones. Since the target temperature set for the engine is lower (200-350° C.), it can be obtained in all driving conditions, even the most difficult (typically at low speeds).

The invention is applicable to all internal combustion engines equipped with a particulate filter, diesel engines, lean-burn gasoline engines, etc. It can be used when the catalyst is located upstream of the particulate filter, as in the example described above, as well as when the catalyst is directly implanted in the particulate filter. Additionally and in all cases, an additive to promote regeneration can be added to the fuel. 

1. Exhaust gas line for a motor vehicle internal combustion engine, equipped with a first oxidation catalyst, or pre-catalyst, placed near the engine exhaust exit, and a particulate filter associated with a second oxidation catalyst placed downstream of the pre-catalyst, which comprises first means capable of producing a degradation in combustion efficiency in order to raise the temperature of the gas exiting the engine, second means for generating an exothermic reaction in the pre-catalyst, and third means for generating an exothermic reaction in the catalyst, so as to distribute the task of raising the exhaust gas temperature, required for regenerating the particulate filter, between the engine, the pre-catalyst and the catalyst.
 2. Exhaust line according to claim 1, wherein the degradation in combustion efficiency is achieved by retarding the main fuel injection, i.e., with an injection that is later relative to the top dead center (TDC) of the cycle.
 3. Exhaust line according to claim 2, wherein the main injection is retarded by 2 to 20° crank angle relative to a normal injection.
 4. Exhaust line according to claim 1, wherein the degradation in combustion efficiency is achieved by reducing the quantity of air taken into the engine.
 5. Exhaust line according to any of the preceding claims, wherein the means for raising the temperature of the gas exiting the engine make it possible to obtain gas temperatures between 200 and 650° C. upstream of the pre-catalyst.
 6. Exhaust line according to any of the preceding claims, wherein the means for generating an exothermic reaction in the pre-catalyst are capable of initiating a fuel post-injection phase in the engine. angle.
 7. Exhaust line according to claim 6, wherein the post-injection is late and is between 90 and 240° crank
 8. Exhaust line according to claim 1, wherein the temperature of the exothermic reaction in the pre-catalyst is between 20 and 200° C.
 9. Exhaust line according to claim 1, wherein the means for generating an exothermic reaction in the catalyst is a fuel introduction device located between the pre-catalyst and the catalyst.
 10. Exhaust line according to claim 1, wherein the temperature of the exothermic reaction in the catalyst is between 20 and 300° C.
 11. Exhaust line according to claim 1, wherein the three means for heating the exhaust gas are activated successively according to the difference between the temperature of the gas at the engine exit and the temperature needed at the upstream end of the particulate filter in order to carry out the regeneration thereof.
 12. Exhaust line according to claim 1, wherein at least two of the means for heating the exhaust gas are activated simultaneously.
 13. Exhaust line according to claim 12, wherein the two exothermic reactions are produced simultaneously and controlled so as to achieve the best compromise between HC treatment and fuel consumption.
 14. Exhaust line according to claim 1, wherein, at high engine speeds and medium and high loads, the means for raising the temperature of the gas exiting the engine are given precedence over the other two means for heating the gas.
 15. Exhaust line according to claim 1, wherein control of the heating means is preset by mapping.
 16. Exhaust line according to claim 1, wherein control of the heating means is by closed-loop regulation.
 17. Exhaust line according to claim 16, wherein regulation uses one or more temperatures recorded by sensors at various points in the exhaust line.
 18. Exhaust line according to claim 16, wherein regulation of the means that generate the exothermic reactions takes the exhaust gas flow rate into account.
 19. Exhaust line according to claim 16, characterized in that when the means for raising the temperature of the gas exiting the engine operate by retarding the main injection, regulation acts on the retard angle thereof
 20. Exhaust line according to claim 16, wherein, in order to regulate the exothermic reaction on the pre-catalyst, the quantity and timing of the post-injection is adjusted.
 21. Exhaust line according to claim 9, wherein, in order to regulate the exothermic reaction on the catalyst (8), the average flow rate of the fuel injected into the exhaust is controlled.
 22. Exhaust line according to claim 1, wherein, in order to control the strategy for raising the gas temperature, the preset mapped and closed-loop regulation control modes are combined.
 23. Exhaust line according to claim 22, wherein mapped regulation of engine heating is coupled with regulation by sensor for the exothermic reactions in the pre-catalyst and catalyst.
 24. Exhaust line according to claim 1, wherein, during the regeneration phase, the means for heating the exhaust gas are used continuously.
 25. Exhaust line according to claim 1, wherein, during the regeneration phase, the means for heating the exhaust gas are used intermittently.
 26. Exhaust line according to claim 1, wherein, during the regeneration phase, the means for heating the exhaust gas are used in continuously variable quantities.
 27. Exhaust line according to claim 1, wherein the catalyst is located upstream of the particulate filter.
 28. Exhaust line according to claim 1, wherein the catalyst and the particulate filter are integrated onto the same support.
 29. Exhaust line according to claim 1, wherein the fuel has an additive to promote particulate filter regeneration. 